The proposed research will seek to elucidate some aspects of the biosynthesis of vitamin B12 (B12 biosynthesis) and the metabolism of related compounds. Vitamin B12 is the most recently discovered vitamin, and by far the most complex. Although the molecule shows structural similarities to porphyrins, there are extensive differences from porphyrins and numerous unique additional features. The mode of formation of many of the structural components of B12 remains unknown. It is proposed to study: (a) the mode of incorporation of the 1-amino- 2-propanol group of the molecule; (b) the origin and incorporation of the amino groups of the six amide side chains (amides) of the molecule; (c) the origin and a possible control of formation of nicotinate mononucleotide, which, as the applicant has shown, is the source of the ribose of the N-gamma-glycosidic nucleotide of the molecule; (d) studies on delta-aminolevulinate and methionine, known B12 precursors, in B12- producing bacterial systems, in vitro; (e) the enzymology of the interconversion of complete corrinoids, the process which occurs when a free base corresponding to one complete corrinoid is given to bacteria containing another complete corrinoid. The proposed topics entail the growth of B12-producing bacteria, and the study of their enzymes and enzyme systems. Paper chromatographic and paper electrophoretic separatory techniques, and spectrophotometric methods, direct or coupled to other enzymes, will be used with radioactive and/or with organically synthesized substrate molecules and inhibitors.